Too many bujinkan practitioners are not flexible enough and they should spend some time outside the dôjô to improve their body. The dôjô is where you learn the waza, everything else is your responsability and should be done on your free time. Bujinkan instructors are not body fitness teachers.
At 50, I still smoke*, I eat meat and drink alcohol reasonably* and if I am a little overweight* I still keep my body flexible because in life everything is about balance and flexibility. So, if you are young, if you don’t smoke, if you are a vegetarian and do not drink, and if you have the perfect BFR**, you have no excuse.
You train because you have chosen to do so and no one has been forcing you. So please train your flexibility as it will definitely change your taijutsu.
Be Happy!* Don’t smoke and eat light meals 🙂 **BFR: Body Fat Rate